1. Field
This invention pertains to bolt action firearms and provides a bolt assembly which combines the advantages of a small diameter ninety degree bolt action with the advantages of a sixty degree bolt action.
2. State of the Art
Most firearms include a stock and a barrel with a muzzle end and a breach end mounted to the stock. The barrel is integral or otherwise associated with a receiver in the vicinity of the breach end. A magazine for shells may be associated with the receiver, and a chamber is provided on the breach end of the barrel adjacent the receiver. Cartridges stored in the magazine are fed in sequence through the receiver into the chamber through operation of the "action" of the firearm.
A common form of firearm, particularly rifles, is that known as a "bolt action." Such firearms include a bolt assembly which is operated to chamber a cartridge and lock it into battery position ready for firing. After firing, the bolt assembly is operated to extract and eject the fired cartridge. Usually, such firearms include a magazine with an entry in communication with the receiver of the firearm so that as a spent cartridge is ejected, a fresh cartridge moves up into the receiver between the chamber and the bolt assembly. The bolt assembly is then slid forward to chamber the fresh cartridge and is again locked into battery position.
The bolt assembly serves a number of important functions, and thus includes a number of structural and functional elements. Components carried by the bolt assembly operate in cooperation with other components of the assembly or structures associated with the receiver of the firearm to chamber, extract and eject cartridges in sequence as they are fed from the magazine through the receiver and then to the chamber of the firearm. Other assembly components interact so that during the process of ejecting an extracted cartridge and chambering a fresh cartridge, the action of the firearm is cocked, and in some instances, a safety device is simultaneously moved to a "safe" condition. Accordingly, a typical bolt assembly may include a bolt body which is usually approximately cylindrical and mounted with its longitudinal axis approximately parallel the longitudinal axis of the barrel, a bolt handle extending from the bolt body, a bolt handle pin (for fastening the bolt handle to the bolt body), a bolt head which carries locking lugs or other suitable locking mechanisms, a bolt head key pin for coupling the bolt head to the bolt body, a bolt shroud for housing various firing pin components, and a number of ancillary components necessary for the extracting, ejecting and firing functions of the firearm, including various springs, pins, sears, and washers.
It is conventional practice in a bolt assembly to include a gas stop subassembly with projections configurated approximately the same as the locking lugs on the bolt head. The gas stop projections thus enter the locking lug grooves following the locking lugs and remain in position in those grooves when the bolt body is rotated to urge the locking lugs into engagement with locking structure associated with the receiver. The gas stop subassembly is thus fixed longitudinally with respect to the bolt body, but is mounted to permit rotational movement of the bolt body while the gas stop projections remain in place within the lug grooves.
The multiple functions and components required of a bolt assembly impose constraints on its design. Heretofore, designers have been compelled to make choices and compromises to the detriment of some of the preferences gun operators (shooters) hold for specific features. For example, it is considered desirable that a firearm be as lightweight as practicable consistent with the requirements of durability and reliability. In the specific case of a bolt action firearm, a balance must be drawn among several factors in determining the amount of rotation required of the bolt assembly or the bolt body by operation of the bolt handle. Because rotation of the bolt is relied upon for cocking action, sufficient rotation should be provided to effect this action without undue force requirements. On the other hand, if too much rotation is required to release the bolt from its battery position, an undue amount of time is required for ejecting the spent cartridge and loading a fresh cartridge.
Experience has shown that ninety degrees of rotation, while acceptable, tends to be unduly time-consuming and imposes undesirable limitations on the available mounting positions of a scope. Ninety degrees of bolt rotation does, however, permit the location of locking lugs such that they may be oriented in non-interfering locations with respect to a magazine when the bolt is withdrawn through the receiver during the ejection and reloading cycle of the bolt assembly. For this reason, relatively light-weight bolt assemblies utilizing small diameter bolt bodies are feasible with ninety degree bolt assemblies.
A more ideal bolt assembly from the standpoint of operational features, notably rapid loading and close mounting of scopes, is an assembly which permits unlocking from battery position with a sixty degree rotation of the bolt body. Such assemblies, commonly referred to as "short throw bolts," "sixty degree bolts," or "sixty degree bolt assemblies" may actually rotate somewhat less than or more than sixty degrees, but utilize rotations sufficiently close to sixty degrees to be readily distinguished from ninety degree bolt assemblies.
One of the advantages of sixty degree bolt systems is the utilization of radially spaced locking lugs. Typically, three such lugs are provided in a set on the perimeter of the bolt head straddling radii spaced approximately 120.degree. from each other. The lugs occupy approximately half the perimeter of the cross-section of the bolt head and provide a good uniform bearing surface to resist the explosive forces generated in the chamber of the firearm when the gun is fired. Sometimes, a plurality of sets of lugs is provided to increase the explosion-resisting bearing surface area.
The necessary or desirable location of other components of the bolt assembly, as well as other design considerations of a firearm, establish the practical orientations of the locking lugs when the bolt assembly is in its unlocked condition. Inevitably, the travel path of one of the lugs as the bolt assembly is withdrawn from battery position rearwardly to eject a spent cartridge, crosses the entry of the magazine. That is, one lug, which may be regarded as a "bottom" lug, is inevitably oriented downwardly during the reloading operation of the firearm. Typically, the magazine is located beneath the receiver so that fresh cartridges are inserted upward into the receiver as the bolt is withdrawn past the magazine location. The locking lug carried by the bolt head is oriented down to register with a locking lug groove in the bottom of the receiver portion of the gun directly behind the chamber. Because of this necessary orientation of the locking lug, it has been considered essential in sixty degree bolt assemblies that the diameter of the bolt body be sufficient to hold cartridges down into the magazine below the level of the locking lug. Otherwise, cartridges would rise up into the receiver sufficiently to interfere with the lug during its rearward travel. To avoid this difficulty, it has been conventional practice to provide bolt bodies of the same or greater diameter than the locking lugs for sixty degree bolt assemblies. These large diameter bolt bodies add weight and require a somewhat larger receiver than is customary for ninety degree bolt assemblies.
There remains a need in the firearms art for a bolt assembly which offers the advantages of a sixty degree bolt assembly without the attendant disadvantages imposed by a large diameter bolt body.